Hibiscus cannabinus L. (kenaf) is a biennial and short-day herbaceous plant cultivated for soft bast fiber in the stem. It belongs to the family of Malvaceae, which is notable for economic and horticultural importance. Kenaf possessed a long history of cultivation in India, Bangladesh, Thailand, parts of Africa, and to a small extent in southeast Europe. Grown over 4000 years in Africa, different parts of kenaf tree have been served as the sources of food, animal diet, handicraft making and fuel to the local communities. Several species are found growing widely in many countries. At the present, principal farming areas are throughout China, India and many other countries including Mackay, Australia; Texas, USA (seed farms) and Tamaulipas, Mexico.
In Malaysia, kenaf is receiving an increasing attention from manufacturers due to its broad applications in fiber board, biocomposite materials and high protein animal feed makings. Malaysian government is interested to cultivate kenaf as the fourth industrial crop in the nation in order to replace tobacco plantation and achieve agricultural diversification. Researches on kenaf production in Malaysia were initiated in early 2000 and first kenaf seed production undertaking was carried out in Serdang, Selangor. However, the cultivation of kenaf in Malaysia is still at experimental stage and the plant is still not optimally utilized by the industry. For instance, kenaf seeds that contain considerable oil content with possible nutraceutical values are disposed as waste material during the harvesting or processing of kenaf.
Physically, kenaf seeds are relatively small (6 mm long×4 mm wide), slate-black in color and triangular in shape with acute angles. Kenaf varieties produce a number of seeds that range from 36,000 to 40,000 seeds/kg. The yield of kenaf seeds is highly dependent on the variety and cultivating location of the seed. In Malaysia, the seed yield is only approximately 700 kg/ha at present. If the consistent seeds yield of 1500 kg/ha could be obtained, kenaf might be a profitable oilseed crop on the basis of 20% oil extraction.
Oil composition of kenaf seed is very similar to cottonseed except for the presence of gossypol (a toxic phenolic pigment) in cottonseed oil. Kenaf seed oil (extracted by Soxhlet extraction) is high in unsaturated fatty acids (76.0%-81.5%) with linoleic acid (C18:2) being the predominant fatty acid (45.9%) in the oil. Besides, kenaf seed oil is also high in phospholipids and phytosterols (6.0% and 0.9% of the oil, respectively). Owing to the considerable oil content and unique composition of kenaf seed oil, it has been suggested in the prior art that kenaf seed oil may present as an alternative and economical source of edible oil for human consumption.
However, oils that are extracted by using organic solvents such as n-hexane or petroleum ether are always doubted for its safe consumption. Hence, supercritical carbon dioxide fluid extraction (SFE) seems to be a good solution in this scenario. SFE offers the usage of non-toxic, non-explosive, environmental friendly, cost effective, time saving and selectivity-adjustable solvent (supercritical carbon dioxide fluid) in the extraction advantageously. Moreover, it also enables the oil extraction to be carried out at low temperatures and complete removal of solvent at the final stage of the extraction.